Oral Motor Therapy
Here are some exercises you might be interested in doing with your child to improve the muscles in their mouths and hopefully, along the way, improve clarity and ease of speech.
The PDF below has been taken from a speech therapy site: wiebrecht.weebly.com - this is just one PDF of many speech therapy exercises. Worth taking a look.
The PDF below has been taken from: http://www.treasureforteachers.com/yahoo_site_admin/assets/docs/teachbookport.248231804.pdf and contains Tongue exercises and other activites.